Firewall Forward

December 11, 2012

Hardware for the Cabin Heater - 2.0 Hours

Okay, it's back to reality. Time to get some work done here. I'm thinking there's one more little item I really want to take care of before I rivet the firewall recess in place on the firewall. Just below the recess, right inside the firewall, the cable for the cabin heater valve comes in. The end is held in place with some simple hardware. But it also passes through a hole in one of the firewall stiffeners. I figure it's going to be a whole lot easier to locate and drill that hole, and put the hardware in place now, before riveting the firewall recess in place. So tonight I got busy to do just that. Here's the relevant drawing, and the hardware layout I came up with. The hardware is shown in exactly the sequence I installed it in place. First the bolt comes through, then a stainless washer, then a short piece of tubing used as a standoff (about 1/4"), another washer, the clamp, and finally a washer and locknut.

The print is too small to see in this pic, but it calls for a #10 hole in the stiffener, where you can see the cable passing through. Then a clamp holds the end of the cable in place. I decided to use the bolt that's already there to hold the heater valve in place. Actually, I put in a longer one, in this case an AN3-6A. This allows me enough length to put a short piece of tubing on it as a standoff, so the clamp is positioned out from the firewall to capture the cable at approximately the same distance out from the firewall as the hole in the stiffener puts the cable. I hope that makes sense. In other words, the cable remains straight with no kink or bend caused by the clamp pulling it toward the firewall. Without the standoff, the clamp would do just that. This seems like a much more sensible solution.

Here's a shot from the inside, after the hole in the stiffener was drilled, cleaned up, and everything put together:

You can see the hole through the stiffener, and the hardware in place for the cable. Nice straight line, right in line with the attachment point on the heater valve. I don't actually have the heater cable yet so I can't try it out. But even if I did have the cable, I won't know the exact length to cut it to until I have my panel planned out. When I get to that point, it will be a simple matter to slip the cable into place and hook it up here. The hard part is done.

By the way, the plans call for the hole through the stiffener to be at a higher point, roughly 1-3/32" below the recess opening. I drilled mine lower, as seen here, so it's in a straight line with the valve and the clamp. The distance of this hole is roughly 1-7/8" below the recess. This makes more sense to me.

Next, I cleaned up the firewall recess and squeezed some sealant into the corners and the bend area, where there are some holes that you don't want engine compartment fumes to come through. I didn't get a picture. I'll have one next time. I wanted to get that done so it can cure over the next couple of days.

I'm very happy to have this little task finished now. It was indeed much easier, especially drilling that hole, with the access through the opening still available. I think I'm FINALLY at a point where I'm ready to rivet the firewall recess in place. I'm going to sleep on it, since I'm out of time tonight anyway, and try and see if I can think of any reason not to proceed.